NU321-ECP bearing: complete specifications & equivalents
The NU321-ECP is a ISO 15 radial bearing sized 105 x 225 x 49 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 105 mm |
| Outer diameter D | 225 mm |
| Width B | 49 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | polymer (PA66 glass-fibre reinforced) |
| Basic dynamic load rating C | 500 kN |
| Basic static load rating C0 | 500 kN |
| Fatigue load limit Pu | 57 kN |
| Reference speed (thermal) | 3200 rpm |
| Limiting speed (mechanical) | 3800 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 8500 g |
| Manufacturer designation | SKF NU 321 ECP |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 6.1 single-row cylindrical roller bearings |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 6.1 single-row cylindrical roller bearings) · extracted 2026-09-26
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 6.1 single-row cylindrical roller bearings); SKF® and SKF Explorer® are trademarks of AB SKF, used here for identification only — mpnbase is not an authorized SKF distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at skf.com.
Dimensions in inches & NU300-series range
| Bore d | 4.134 in |
|---|---|
| Outer diameter D | 8.858 in |
| Width B | 1.929 in |
| ISO bore code | 21 |
| Radial section height (D−d)/2 | 60 mm |
| Smallest bore in NU300-series | 17 mm |
| Largest outer diameter in NU300-series | 620 mm |
| Width range across NU300-series | 14–109 mm |
| Bore position in NU300-series (smallest first) | 19 of 33 |
| Bore above smallest NU300-series size | 88 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| N321-ECP | SKF | full Dimensions and internal design equivalent — standard interchange. | Same ISO 15 envelope 105×225×49 mm and equivalent catalogue ratings; the N execution differs in flange/retaining-ring configuration — boundary-dimension interchangeable, but axial-locating behaviour is not identical. |
| NJ321-ECP | SKF | full Dimensions and internal design equivalent — standard interchange. | Same ISO 15 envelope 105×225×49 mm and equivalent catalogue ratings; the NJ execution differs in flange/retaining-ring configuration — boundary-dimension interchangeable, but axial-locating behaviour is not identical. |
Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.
How the NU321-ECP model number is decoded
For a 105 mm shaft, SKF lists NU321-ECP as single-row caged cylindrical roller: 225 mm OD, 49 mm wide, Pu 57 kN, the catalogue lists 3,200 r/min thermal reference speed and 3,800 r/min mechanical limiting speed. The NU configuration means two integral flanges on the outer ring and no flanges on the inner ring, so the inner ring together with the roller set is separable; functionally the bearing is non-locating: the inner ring assembly can float axially in both directions and the bearing cannot support axial load. Reading the order-string suffix ECP: the E-design execution with a glass-fibre reinforced polyamide (PA66) cage, limited to 120 °C continuous. With C 500 kN and C0 500 kN, size the bearing on the 105×225 mm ISO 15 envelope and check the 57 kN Pu against the equivalent-load floor; the catalogue lists 3,200 r/min thermal reference speed and 3,800 r/min mechanical limiting speed. Assembly note: fit the inner ring and roller assembly onto the shaft and the outer ring into the housing independently; thermal expansion is absorbed by axial float, so do not trap the inner ring between shaft shoulders. Heat steel rings inductively to max 120 °C — the PA66 cage sets the ceiling.
Typical equipment & failure modes
Common applications
- rolling-mill auxiliary drive shafts
- paper-machine press rolls
- cement-plant conveyor drives
- heavy gearbox and pinion shafts
Known failure patterns
- inner-ring raceway spalling from overload or contamination in the line-contact hertz zone
- outer-ring raceway fatigue after extended service at loads above the catalogue L10 rating
- polymer cage softening above 120 °C
- cage pocket wear from roller skidding at insufficient radial load or during start-up before oil film build-up
- roller-end scoring from inadequate oil flow in the roller-raceway contact
- edge-loading fatigue after shaft deflection beyond the 3–4 minute alignment limit
- rolling-contact fatigue spalling after the rated L10 life is exceeded
Selection pitfalls — read before you substitute
- Do not use a NU bearing where axial load must be carried — the design carries radial load only
- The dimension series 3 (medium-section ISO 15 envelope) envelope is shared with the N/NU/NJ/NUP executions of 321, but flange configuration and axial-locating behaviour differ — quote the full SKF NU 321 ECP and do not substitute rib styles without checking the shaft locating scheme.
- Press-fit force goes through ring faces only; driving a ring home through the rollers brinells the 225 mm raceway.
- Shaft and housing fillets must clear the bearing chamfers; an oversized radius tilts the 49 mm-wide ring and concentrates load.
- The 500/500 kN ratings are SKF catalogue 17000 (2018) values for the ECP execution; re-verify against the current catalogue for critical drives and keep the catalogue version with the specification.
Frequently asked questions
What are the dimensions and catalogue data of NU321-ECP?
SKF NU 321 ECP is a single-row caged cylindrical roller bearing with 105 mm bore, 225 mm OD and 49 mm width per ISO 15. SKF lists C 500 kN, C0 500 kN, Pu 57 kN, reference speed 3,200 r/min and limiting speed 3,800 r/min, mass about 8500 g.
What does the NU designation and ECP suffix mean?
The ECP suffix marks the E-design execution with a glass-fibre reinforced polyamide (PA66) cage, limited to 120 °C continuous. Structurally this execution has two integral flanges on the outer ring and no flanges on the inner ring, so the inner ring together with the roller set is separable.
Can NU321-ECP take axial load and locate the shaft?
No — the inner ring has no flanges, so the NU bearing is non-locating and carries radial load only; use NJ (one direction), NUP (both directions) or a paired thrust bearing for axial duty.
How does NU321-ECP compare with the other executions in the same envelope?
The N/NU/NJ/NUP executions share the ISO 15 envelope and load ratings but differ in flange arrangement and axial-locating behaviour; quote the exact order number.
What limits the service life of this bearing most often?
Line-contact fatigue above the L10 rating, cage wear at light loads and high temperatures, and edge loading from misalignment beyond about 3–4 minutes of arc are the typical failure drivers.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 6.1 single-row cylindrical roller bearings on 2026-09-26. Read our editorial & correction policy.